The proposed research project will provide insights into the mechanisms of oncogene activation in chemically-induced and spontaneously occurring rodent tumors as well as some selected human tumors. Understanding oncogene activation will add to our knowledge of how chemicals induce a carcinogenic effect. This information will be valuable in the establishment of approaches to utilize data on oncogene activation and expression in risk analysis of chemical carcinogens . This may provide a possible new approach to increase the sensitivity of chronic animal test for detection of carcinogens. In addition, such work may eventually allow us to classify carcinogens according to their mechanism of action and further enhance our ability to estimate accurately the risk of cancer in humans exposed to carcinogens.